1. Field of the Invention
The present invention relates to a method of eliminating home-in noise generated when an optical pickup of an optical disc drive is moved to a home-in position. More particularly, the present invention provides a method of eliminating noise generated during home-in of an optical pickup in an optical disc drive using a variable step counter and having no home limit switch.
2. Description of the Related Art
As is known, optical discs are generally classified into two familes: compact discs (CDs); and digital versatile discs/digital video discs (DVDs) suitable for multimedia use.
Optical disc drives use an optical pickup to radiate a laser beam onto an optical disc rotated by a spindle motor, and to detect a laser beam reflected from the optical disc, in order to record data onto and/or read data from the optical disc.
As shown in FIG. 1, an optical disc drive 100 includes a spindle motor 110 which rotates an optical disc 130, an optical pickup 120, and a stepping motor 140 which drives the optical pickup 120. The optical pickup 120 includes a focusing actuator (not shown) which is used to focus a laser light beam onto a recording surface of the optical disc 130, and a tracking actuator (not shown) by which the focused laser beam is able to follow tracks on the optical disc 130. Since the tracking actuator has a limited range of movement, the tracking actuator uses the stepping motor 140 to move the optical pickup over larger distances. In general, the optical disc drive 100 includes a step counter (not shown) which counts steps associated with the operation of the stepping motor 140.
When power is applied to the optical disc drive 100, it performs a home-in operation to move the optical pickup 120 to an initial position in order to set a movement start point. The type home-in operation depends on the type of the optical disc drive 100. For example, when the optical disc drive 100 includes a home limit switch, the optical pickup 120 moves up to a home position at which the home limit switch is turned on. In contrast, when the optical disc drive 100 does not include a home limit switch, the optical pickup 120 is moved into contact with an outer wall of the spindle motor 110 where a value of the step counter is reset to zero in order to return to a home position, so that an absolute value of the step counter corresponding to a physical position of the optical pickup 120 corresponds to the stepping motor 140.
As described above, when power is applied to the optical disc drive 100, the optical disc drive 100 generally performs a home-in operation before a requested operation such as, for example, reading or recording.
When the optical disc drive 100 includes a home limit switch, the optical pickup 120 is easily controlled to return to a home position. However, the home limit switch may complicate the configuration of the optical disc drive 100 and increase the cost of manufacturing the optical disc drive 100.
In order to solve these problems, the related art suggests a method of moving the optical pickup into and against an outer wall of a spindle motor and setting a step counter value of a step motor to zero. Without the forced clash of the optical pickup against the spindle motor, the exact position of the optical pickup is not known, and thus an absolute step counter value cannot correspond to the position of the optical pickup. Thus, the forced clash is used to obtain the absolute step counter value corresponding to the position of the optical pickup.
Home-in noise is generated by the forced clash of the optical pickup against the spindle motor. In an optical disc drive using a fixed step counter depending on the position of the optical pickup, such home-in noise cannot be avoided.
As used herein, a forced home-in refers to a method of forcibly clashing an optical pickup against an outer wall of a spindle motor to reset a step counter during application of power, and then moving the optical pickup to a home position. As used herein, direct home-in refers to a method of allowing an optical pickup to directly move to a home position without clashing against an outer wall of a spindle motor when a tray is opened. The forced home-in and the direct home-in are performed in an optical disc drive without home limit switch.
Initial operations of the optical disc drive to which power is applied will now be described.
1. Set input and output ports of a microcomputer for controlling the optical disc drive, initialize an interrupter and a timer of the microcomputer, reset a digital signal processor (DSP), arrange flags necessary for a servo, and initialize each part such as the DSP, the servo, and the like.
2. Attempt a forced home-in in a micro step mode or a half step mode in order to allow a step counter value to correspond to the position of the optical pickup. Move the optical pickup to an inner circle by about 3000 micro steps (40 mm), which generates home-in noise. Reset the step counter value to zero. Depending on the type of the optical disc drive, the optical pickup may move to an outer circle to find a home position (00:02:00 where the step counter value is about 214) or stay at the inner circle position. Depending on the type of the optical disc drive, the optical pickup may try a forced home-in when a tray is opened and closed, so as to reduce noise. In this case, noise from the tray covers forced home-in noise. However, noise generated when the tray is opened and closed may be problematic.
3. Perform automatic adjustment, read table of contents (TOC) to obtain information on the optical disc drive, and calculate a linear velocity, a track pitch, and so forth.
4. Finish lead-in and then enter a pause mode.
As described above, in an optical disc drive without home limit switch, a step counter value corresponding to the physical position of an optical pickup is determined as an absolute value, and thus noise caused by forced home-in cannot be avoided. In other words, since the step counter value does not vary depending on the position of the optical pickup during application of power, noise is generated during the forced home-in.
In most optical disc drives, after the optical disc drive is driven, an optical pickup always moves to a home position and then a tray (direct home-in) is opened, since the home position is always a basis. The direct home-in is achieved by two methods. The first method is to move the optical pickup to the home position through an access of the optical disc drive. The other method is to move the optical pickup by steps corresponding to a value obtained from subtraction of a step counter value in the home position from a step counter value in a current position and then open the tray.
The aforementioned methods of direct home-in are not without problems. The first method has a problem in that since the optical pickup moves through the access, a fail of the access may delay opening the tray. The problem of the second method is that only large step-out and deviation of a step motor are checked during a long-term access test. Of course, since most optical disc drives have a routine to check step-out, a step counter value is recalculated when step-out occurs. However, in a case where a slight step-out occurs and a fixed step counter is used in the second method, an optical pickup goes to another position instead of going to a home position, or does not properly perform direct home-in when a tray is opened. The access test may not be properly performed due to a difference of the position of the optical pickup from a step counter value. These problems result from mapping a step counter value corresponding to the position of the optical pickup to an absolute, fixed value.